1. Field of the Invention
The present invention relates generally to a Multiple-Input Multiple-Output (MIMO) communication system, and in particular, to a MIMO data transmission method for improving spectrum efficiency using a data multiplexing technique.
2. Description of the Related Art
The increasing demand for various broadband services such as high-speed Internet access and high-quality video services as well as the recent development of semiconductor and display device technology. There is ongoing research to more efficiently utilize the limited frequency resources for broadband wireless data transmission service in the 3rd generation (3G) and 4th generation (4G) mobile communication technology fields. Various techniques such as Spatial Division Multiple Access (SDMA), Space-Time Coding (STC), and Beam Forming based on a MIMO antenna system have been recently provided toward this end.
The MIMO system uses the STC technique to divide a channel into a plurality of independent spatial channels using multiple transmission antennas and multiple reception antennas and to secure the capacity.
A Vertical Bell Labs Layered Space Time (V-BLAST) algorithm, which is a well-known MIMO technique, can obtain spectrum efficiency of 20 to 40 bps/Hz for actual signal-to-noise ratio (SNR) range and bit error performance in an indoor rich scattering propagation environment. The high spectrum efficiency results from a multiplexing gain by parallel data transmission. The V-BLAST technique uses its unique detection algorithm different from the joint detection algorithm. That is, the detection algorithm of the V-BLAST technique first decodes the highest-power signal, and continuously decodes the highest-power signal among the signals remaining after canceling an influence of the decoded signal from each of the received signals. Such a decoding method is called optimum ordering (OR) and successive interference cancellation (SIC).
However, in order to increase the spectrum efficiency, the V-BLAST technique simultaneously transmits independent data streams via multiple transmission antennas, so a receiver suffers inter-channel interference (ICI) and the ICI increases with the number of the transmission antennas.
In addition, the V-BLAST technique is inoperable when the number of transmission antennas is greater than the number of reception antennas. Further, the V-BLAST technique cannot expect high performance even when the number of transmission antennas is equal to the number of reception antennas.